Batman: Arkham City - Acts of Violence

For this mission, you actually just have to save Politcal Prisoners scattered around the city who are being attacked. You'll hear them yelling for help and a little marker should appear on the map as long as you're nearby. This is actually pretty simple for the most part. Just make sure you save them as you find them so you don't have to find them again later. I don't believe there are a set number of these so just keep wandering and you'll find them. And when you go to save someone, it's usually just a single enemy who will be holding the guy against a wall making him very easy to sneak up on. Just watch for random enemy spawns nearby.